1. Field of the Invention
The present invention relates to a method of and an apparatus for carrying out data communications between portable information terminals, and more particularly to a method of and an apparatus for carrying out data communications between portable information terminals through a wireless communication medium such as infrared radiation with an energy source which may either be a battery of limited capacity housed in each of the portable information terminals or an external power supply of unlimited capacity.
2. Description of the Related Art
One known portable information terminal, as disclosed in Japanese patent application laid-open No. 63-246048, which is used in a wireless signal transmission system which employs a wireless signal such as a radio signal for transmitting data between main and auxiliary units, transmits data at different transmission rates depending on the condition in which the wireless signal is propagated. Such a portable information terminal is usually powered by a battery, and communicates with another terminal through a wireless communication medium such as infrared radiation. Generally, the portable information terminal consumes a large amount of electric energy for wireless communications through infrared radiation, and the incased battery of the portable information terminal has a limited capacity because the portable information terminal is relatively small in size and light in weight. Consequently, the portable information terminal which effects wireless communications through infrared radiation cannot be used continuously for a long period of time due to the limited battery capacity.
The wireless signal transmission system disclosed in the laid-open no. 246048/1985 is capable of increasing the reliability of data transmission by varying the data transmission rate according to the propagation condition of the wireless signal. However, the disclosed wireless signal transmission system gives no solution to prevent the high consumption of the electric energy of the portable information terminal without degrading the efficiency of the data transmission.